move contrasting_text_color() into ArdourCanvas

1 files changed, 32 insertions, 0 deletions

diff --git a/libs/canvas/utils.cc b/libs/canvas/utils.cc
index bdc8fad039..99516c849b 100644
--- a/libs/canvas/utils.cc
+++ b/libs/canvas/utils.cc
@@ -220,3 +220,35 @@ ArdourCanvas::distance_to_segment_squared (Duple const & p, Duple const & p1, Du
 	return ((dpqx * dpqx) + (dpqy * dpqy));
 }
 
+uint32_t
+ArdourCanvas::contrasting_text_color (uint32_t c)
+{
+	double r, g, b, a;
+	ArdourCanvas::color_to_rgba (c, r, g, b, a);
+
+	const double black_r = 0.0;
+	const double black_g = 0.0;
+	const double black_b = 0.0;
+
+	const double white_r = 1.0;
+	const double white_g = 1.0;
+	const double white_b = 1.0;
+
+	/* Use W3C contrast guideline calculation */
+
+	double white_contrast = (max (r, white_r) - min (r, white_r)) +
+		(max (g, white_g) - min (g, white_g)) + 
+		(max (b, white_b) - min (b, white_b));
+
+	double black_contrast = (max (r, black_r) - min (r, black_r)) +
+		(max (g, black_g) - min (g, black_g)) + 
+		(max (b, black_b) - min (b, black_b));
+
+	if (white_contrast > black_contrast) {		
+		/* use white */
+		return ArdourCanvas::rgba_to_color (1.0, 1.0, 1.0, 1.0);
+	} else {
+		/* use black */
+		return ArdourCanvas::rgba_to_color (0.0, 0.0, 0.0, 1.0);
+	}
+}